Advances in electronics packaging techniques are allowing modern control electronics to be packaged with increasing density and to be placed into more hostile environments. In many cases, integrated electronic control circuits are being packaged with the high power switching transistors that they control. These packages are then included in higher level assemblies, often with other power dissipating elements. Examples of such systems are modern automotive ignition interface circuits that control the switching, monitoring, and control of ignition coil currents. These systems typically employ one or more high power switching devices, such as an Insulated Gate Bipolar Transistor (IGBT), power MOSFET, or the like, coupled to, and driven by, a low power ignition control circuit. These systems are often packaged in over-molded plastic packages which are then embedded in individual ignition coil packages. In operation, such systems generate heat mainly as a result of power being dissipated in the IGBT and/or other power switching devices during closed-loop controlled limiting of one or more ignition coil currents. The coils themselves also generate heat which may be transferred to the control electronics. Under some operating conditions, such as during excessively long “on” or “dwell” times, the operating temperatures of these electronic components can exceed maximum allowable levels, resulting in damage or destruction of the power switching device and/or ignition coils.
This invention is directed to a system and circuitry for dynamically regulating the temperature of a power switching device while maintaining the device operational so that the operating temperature thereof does not exceed a predefined temperature limit.